This invention relates in general to reaction engines and in particular to a new and useful axially semisymmetrical supersonic air intake for reaction engines and particularly solid fuel ram jet rocket engines.
In aircraft missiles flying at high Mach number speeds, a supersonic diffuser transforms the high kinetic energy of the inflowing air into pressure energy, while decreasing the air velocity. In ram jet engines this is performed by the supersonic diffuser alone. The air thus compressed is then used in the combustion chamber for the combustion.
According to experience a particular intake disturbance occurs in supersonic diffusers, which is termed "humming" in the art. This disturbance occurs under highly "subcritical" conditions. The fact is that the compression shock which has already migrated into the zone in front of the cowl lip of the intake channel failed to assume a stable position and oscillates back and forth in a non-steady state.
This leads to strong variations in the flow and thus to a considerable drop of the mean effective pressure and of the rate of air flow. The disadvantage resulting therefrom decidedly require a suppression of this abnormal operating condition. Frequently, the remedy is found in providing the layout point somewhat in the supercritical zone, not in the theoretically advantageous critical operating point mentioned above. With such a design, the air intake is usually stable, the inflow resistance is low and the pressure gain is satisfactory.
A particular measure for securely eliminating the undesirable humming, even in extraordinary flight situations encountered with ram jet engines at supersonic speeds, is disclosed in German OS 28 01 119, and comprises providing bleed air apertures on the surface of the displacer body in the zone where the vertical external shock produced under strongly subcritical operating conditions is temporarily located and which oscillates back and forth. By allowing the boundary layer in the above-mentioned zone of the intake diffuser or the displacer body to flow off close ahead of the air intake plane, the compression shock is steadied and the humming is prevented. The bleed apertures in the surface of the displacer body communicate with two bleed channels which are separated from each other by a web and open into the boundary layer gap at both sides of the boundary layer plow. The boundary layer plow is designed for keeping the pressure in the boundary layer gap lower than on the surface of the displacer body, i.e. downstream of the first compression shock, but in any case lower than the pressure downstream of the produced vertical shock, where the air then flows away.
The prior art bleed device, aside from having particular advantages in steadying the produced compression shock, has also a certain drawback, namely that the relatively large amounts of air inflowing during the subcritical operating conditions are subjected to two abrupt 90.degree. deflections, once as they enter the bleed channels through the bleed apertures, and then again as they leave the displacer body in the direction of the boundary layer gap and this introduces high resistance to flow and cause losses in the performance. In addition, if a boundary layer plow adjusted to the pressure is used, the outflow area still available at the bottom of the displacer body adjacent the boundary layer gap is too limited for the large amounts of outflowing air.